util/uniq,types/lazy,*: delete code that's now in Go std

sync.OnceValue and slices.Compact were both added in Go 1.21.

cmp.Or was added in Go 1.22.

Updates #8632
Updates #11058

Change-Id: I89ba4c404f40188e1f8a9566c8aaa049be377754
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

version/prop.go

@@ -9,6 +9,7 @@ import (
 	"runtime"
 	"strconv"
 	"strings"
+	"sync"
 
 	"tailscale.com/tailcfg"
 	"tailscale.com/types/lazy"
@@ -174,7 +175,7 @@ func IsUnstableBuild() bool {
 	})
 }
 
-var isDev = lazy.SyncFunc(func() bool {
+var isDev = sync.OnceValue(func() bool {
 	return strings.Contains(Short(), "-dev")
 })